fix(security): don't penalise a correct PIN after a passphrase change

A passphrase change left the PIN vault sealing the old passphrase. The
next PIN unlock opened the vault, walletpassphrase answered RPC -14, and
the generic catch ran the lockout curve on a correct PIN, while Settings
kept showing the PIN as active.

- Passphrase change: when the active wallet's vault exists at completion
  (same vault path as at dispatch, passphrase actually changed), the
  vault is marked out of date for the session and kept on disk: PIN entry
  is no longer offered, a warning toast says so, and Settings shows
  "PIN out of date" with a tooltip on how to fix it. The Change
  Passphrase dialog notes beforehand that a PIN will go out of date.
- PIN unlock: RPC -14 after the vault opened is treated as "PIN out of
  date": passphrase entry, a message, no attempt counted, no lockout, and
  the vault is not deleted (-14 is only the daemon's answer; the vault may
  hold the only copy of a passphrase that opens an older backup). After a
  restart Settings shows the PIN as active until the first PIN attempt.
- A malformed vault (zero-filled by a removeVault() whose unlink failed,
  truncated, unknown version) is treated as missing: passphrase entry,
  "PIN file unreadable", no penalty. New SecureVault::isWellFormed().
- Race guards: Set/Change/Remove PIN are disabled while a passphrase
  change runs, and Change Passphrase while a PIN operation runs.
- Setting or removing the PIN, or switching wallets, clears the mark;
  setting a PIN offers PIN entry again. Change PIN keeps the mark (the
  vault still seals the same passphrase).
- Pure decisions in data/pin_vault_policy.h, unit-tested. New strings in
  all 8 languages.

No vault, wallet or settings format change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app_network.cpp

@@ -1594,6 +1594,7 @@ void App::switchToWallet(const std::string& walletFile, bool stopDaemonConfirmed
     // lock-screen attempt/lockout state + wipe the passphrase/PIN entry buffers — the previous wallet's
     // failed-unlock counter and typed secrets must not apply to the new wallet.
     if (vault_) vault_->setWalletScope(walletFile);
+    pin_vault_stale_ = false;   // the out-of-date mark was the previous wallet's vault
     lock_attempts_ = 0;
     lock_lockout_timer_ = 0.0f;
     lock_error_msg_.clear();
@@ -1696,6 +1697,7 @@ void App::processWalletSwitchRevert()
         settings_->setActiveWalletFile(wallet_switch_prev_file_);
         settings_->save();
         if (vault_) vault_->setWalletScope(wallet_switch_prev_file_);
+        pin_vault_stale_ = false;
     }
     // Clear the crash-wedge so the (good) previous wallet's daemon is allowed to start again.
     if (daemon_controller_) daemon_controller_->resetCrashCount();